Making shaped articles from coke and pitch



Patented Jan. 13, 1942 UNITED STATES PATENT OFFICE MAKING SHAPEDARTICLES FROM COKE AND rrron gan No Drawing. Application August 12,1939,

Serial No. 289,930

6 Claims. (01.2106-284) The invention relates to an improvement in theart of making shaped carbon articles. It relates particularly to animprovement in the manufacture of graphite electrodes.

Shaped carbon articles are customarily made from petroleum coke andpitch. The ingredients are mixed, heated to soften the pitch, and moldedor extruded to the desired form and size, and are then baked tocarbonize the pitch binder. High temperature baking is known to convertthe article to a graphitic form of carbon throughout. Such articles areuseful, for example, as electrodes in the manufacture of chlorine andcaustic soda from salt brine, or of metals from fused metal chlorides.

A graphite electrode should have as high an apparent density aspossible, and as low electrical resistance as possible for mostefiicient operation and to give the longest useful life from a givenelectrode weight. Even slight increases in apparent density andcorrespondingly slight reductions in the electrical resistance of anelectrode are of great practical importance. Thus, a change in apparentdensity from 1.52 to 1.59 is an increase of 5.6 per cent in the mass perunit volume, and indicates an increase in the expected life of theelectrode under otherwise equal conditions. Similarly, a decrease inresistance from 0.00034 to 0.00030 ohm per inch cube represents about a12 per cent electrical savings, in the form of lowered 1 R. loss in theuse of the electrode.

It is accordingly among the objects of the invention to provide animprovement in the art of making shaped carbon bodies from coke andpitch, whereby the apparent density is increased over that usuallyobtained, and the electrical re-- sistance of a graphitized articletherefrom is decreased. Another object is to provide a method ofincreasing the coking power and the melting point of coal-tar pitchwithout unduly increasing the heat and pressure requirements in makingshaped coke-pitch articles therefrom. Yet another object is to provide amethod of modifying the properties of pitch so that its adhesiveness orbinding power in a coke-pitch mixture is increased, and the extrusion ofuniform coke-pitch articles is facilitated.

According to the present invention, coke and pitch, and moreparticularly calcined petroleum coke and coal-tar pitch, each in theproportion and in the state of fine subdivision usually employed inmaking coke-pitch mixtures for the preparation of shaped carbonarticles, are mixed at or near room temperature with a minor proportionof a polychlorinated hydrocarbon, and preferably from 0.7 to 6 per centof carbon tetrachloride, or of acetylene tetrachloride, based on theweight of pitch present. The coke-pitchchloro-hydrocarbon mixture isthen heated to a reaction temperature above the initial melting point of'the 'pitchbut below a carbonizing temperature, and mixed at thistemperature to provide a uniform composition of the desired consistencyfor a period suitably in the range from 10 to 45 minutes and preferablybetween 15 and 30 -minutes. The so-treated mixture is cooled and thenmolded or extruded, and finally heated sufficiently to carbonize thebinder or to graphitize the entire body of carbon present. If desired,pitch may be reacted with carbon tetrachloride and then mixed with cokein the usual manner.

' Graphite articles formed according to the present improved method havehigher apparent density and lower electrical resistance than thoseprepared without the use of the carbon tetrachloride or equivalentchloro-hydrocarbon. This is believed to be due to a reaction of carbontetrachloride on pitch at temperatures above the initialmelting point ofthe pitch. This reaction increases the free carbon content, the cokingpower, and the melting point of the pitch, and decreases to a certainextent the loss due to volatile matter during the carbonizing operationapplied to the pitch-coke article. It also increases the adhesiveness ofthe pitch, and facilitates the extrusion of coke-pitch articles.

The following table illustrates the effect of carbon tetrachloride onpitch. In the reported experiments, the indicated percentage of carbontetrachloride was mixed with pitch which had an initial melting point of224 F. (107 C.) and a free carbon content of 29 per cent. The mixturewas heated for from 10 to 20 minutes at a maximum temperature, measuredin the melt, of from 150-180" C., the heating bath being held at about160200 C. In each instance, evolution of hydrogen chloride was observedfrom the pitch-carbon tetrachloride 'mixture. The melting point of thecooled product and its free carbon content were determined.

Table I Increase Sample NO Per cent Fin Rise in Free in free I 0014 M.P. M. P. carbon carbon C. Degrees 1 117 10 33. 4 4. 4 l 120 13 38. 3 9.3 3 43 41. 6 12. 6 3 152 45 41. 7 l2. 7 5 155 48 45. 7 16. 7 10 156 4943.6 14. 6

When the pitches prepared as above, by reaction with carbontetrachloride, were subjected to coking temperatures, it was observedthat loss due to volatility under coking conditions was about 2 per centless when 1 per cent of carbon tetrachloride was employed-than whencoking pared according to the invention. The cokepitch mixtures,containing from 15 to 2'? per cent of pitch, were treated with carbontetrachloride in the manner previously set forth and in amount varyingup to about per cent of carbon tetrachloride calculated on the weight ofpitch.

The average properties of electrodes from three of these series ofpreparations is given in the following Table II, in comparison with theaverage of a similar number of electrodes of the same size (about 180pounds each) made without the use of carbon tetrachloride.

Table II Number Egggg Average Average Group of electetm resistanceapparent trodes chloride ohms/111. density The presence of carbontetrachloride in the pitch-coke mixture not only makes for improvedcarbonized and graphitized articles, but, in spite of the higher meltingpoint imparted to the pitch thereby, permits of the molding or extrusionof shaped articles at moderate working pressures of, for example, from600 to 1200 pounds per square inch, such as are used when no carbontetrachloride has been added to the mix.

The invention has been illustrated with respect to carbon tetrachlorideas the polychlorinated hydrocarbon, and acetylene tetrachloride has beensuggested as among the equivalents for carbon tetrachloride. Thepolychloro-hydro carbon employed need not be a liquid such as thosenamed above, as hexachloroethane and benzene hexachloride, both solids,have been found to exert an advantageous effect on the mixture and toyield graphitized articles of improved characteristics. These and manyother polychloro-hydrocarbons, including chloroform, pentachloroethane,polychlorocyclohexane, and the like, have also been found to give thedescribed reaction.

The present improvement relates as well to the manufacture from coke andpitch of articles wherein the pitch binder is merely carbon! ized as tothose wherein both the binder and the coke are graphitized. It may beemployed with advantage in the manufacture of shaped articles other thanelectrodes, and the composition is capable of being molded as well asextruded to form the improved products.

Other modes of applying the principle of our invention may be employedinstead of the one explained, change being made as regards the methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

We therefore particularly point out and distinctly claim as ourinvention:

A method of treating pitch to increase the binding power thereof incoke-pitch mixtures which comprises heating pitch to a reactiontemperature with a minor quantity of a polychlorinated hydrocarbon, andthereafter carbonizing the sow-treated pitch in admixture with coke.

2. A method of treating pitch to increase the melting point, free carboncontent and coking power thereof, and to increase its binding power incoke-pitch mixtures which comprises heating the pitch to a temperatureabove its melting point with from 0.7 to 6 per cent of its weight orcarbon tetrachloride, and thereafter carbonizing the so-treated pitch inadmixture with coke.

3. 'I-he nethod of making shaped articles from coke and pitch whichcomprises mixing finely divided coke and finely divided pitch with aminor quantity of a polychlorinated hydrocarbon, heating the mixture toa temperature above the initial melting point of the pitch but below acarbonizing temperature, shaping the resulting mixture, and heating theshaped article to carbonize the binder.

4. Themethqd of making shaped articles from coke and pitch which;comprises mixing from '73 to parts of finely divided petroleum coke withcorrespondingly from 27m 15 parts of finely divided coal-tar pitch anda, minor quantity of carbon "tetrachloride, heating the mixture: to atemperature at which carbon tetrachloride reacts with pitch above theinitial, melting point oi the-pitch but below a carbonizing,temperature, shaping the resultingmixture and heating the shaped articleto carbonize thebinder.

5. The method of making shaped articles from coke and pitch whichcomprises mixing fromf73 to 85 Parts of; finely divided petroleum cokewith correspondingly-fromz'l to 15 parts of, finely d1- videdcoal-tarpitch and from; 0.7 to 6 per cent, based onthepitchweight, of carbontetrachloride, heating the mixture to a temperature at which carbon,tetrachloride reacts with pitch above the initial melting pointof-thepitch but e ow be z netemperature, shapin the reu n mixtu e andeatin e shaped article to b nize he b nder The methfld: as c a m neleimw ere n e hekinai ar ied, o aphitizi s pera r s i9. e nh t e. b t hecokeand the binder, therebyto produce an article of higher appar ent densityand lower electricalresistance than have, articles produced inglikmanner; but With'- tihe c b m t a eride.

i EDWARD COLE.

. RIGHABD I. 'IHRUNE.

